The final piece to get my eeepc to take pictures periodically was to wrap up the vlc (see Webcam capture using vlc) and crontab (see Crontab) stuff in a bash script. This is a way of making scripts for the Unix shell which is default on many distributions and certainly on Ununtu.
This is the script I entitled capture.sh, put in my bash_scripts folder and referred to with the crontab:
# If the date directory does not exist, create it
if [ ! -d $D1 ] ; then
mkdir -p $D1
#cd to this new directory
# capture images using vlc
cvlc v4l2:// -V image --image-out-ratio 150 --image-out-prefix $D2 --run-time 50 vlc://quit 2> /dev/video0